The 39-strong tour group from Harrow, who know each other through Latin ballroom dancing classes, boarded the vessel, Lady Anne, in Rudesheim, western Germany, on Saturday evening.

But by Monday morning many of the passengers had been taken ill and paramedics were called to treat one couple when the ship docked in Boppard.

Mr Lanning said: "There were a number falling sick. We were called into the lounge to be told it was a norovirus. The doctor reported back that it was an epidemic.

"Those who came onto the boat from outside were wearing protective suits and masks.

"Those of us who were well were able to go into the lounge. Those who were sick were consigned to their cabins.

"People had sickness and diarrhoea. Vomit and excrement were all over the place. The smell from it was awful."

Several holidaymakers were taken to local hospitals and German health officials quarantined the boat.

On Wednesday morning, passengers were transferred on to coaches to make their way to England accompanied - at their insistence - by German paramedics, although three members of the Harrow tour group were still recovering at German hospitals when their friends left.

Three others fell ill on the journey home, including Mr Lanning, who became sick in the Channel Tunnel and had to be met by an ambulance at Dover and taken to hospital in Ashford, Kent.

Reflecting on the ruined cruise, Mr Lanning said: "Only six out of 39 of us remained well. It was a nightmare."

The holidaymakers had paid £329 per person for their five-day trip, but River Cruise Line has apologised and refunded all tickets.

Mrs Lanning criticised the company for a lack of coherent updates during the incident and for failing to disclose to passengers that the previous week's cruise had also been hit by illness, when around 10 people suffered similar symptoms.

The source of the norovirus is yet to be confirmed and the Lady Anne is being decontaminated.

A River Cruise Line statement said: "We would like to again express our gratitude for the excellent work of the German paramedics and offer our apologies to all those directly and indirectly affected.

"When we first identified this as an issue, we worked hard with the ship owners to arrange for deep cleaning and other precautionary measures to be implemented.

"As is often the case, the virus can be very resistant to eradication and despite the measures we undertook, this was the case with this cruise."